Misread your post. If you look at the controller for the content block, the image is saved as a ID:43 or something like that, and a regex string replaces that value with a string that is interpreted from a few variables, I don't have it open at the moment.

Anyways, it builds these paths based on values set in the base.php or interpreted through common assumptions in regards to where files are stored.

I know there was an issue with 5.1 that had a problem with images being inserted, but this has since been fixed as of 5.2 if not sooner in 5.1.1

I work 5.2 version.

If I insert picture from images/ folder which is at the same level as default files/ this is what happens:

Image inserted as image block, which can only reside in files folder have valid URLhttp://mysite/files/LARGENUMfilename.jpg...
that's OK of course.

However, image that is inserted as image while editing content block which is in that images/folder gets this URLhttp://mysite/current_page_where_IMG_is/images/......

I've found where is error.

If I write image path without starting dash, it will reproduce that error.
But image would still be visible while editing.

So ... typing /path/ with dash first should be OK.